High-temperature melting of materials, especially non-ferrous metals, is frequently carried out in either induction furnaces or in gas-fired furnaces in which the gas is burned in combustors arrayed about the crucible containing the charge. Insofar as induction furnaces are concerned, not only are original installations with special power supplies and related wiring very costly, electrical operating energy is also intolerably high.
On the other hand, conventional gas-fired furnaces are often so constructed that contamination by the combustion products of the charge being melted in the crucible is encountered. In fact, to achieve more efficient heating, it is sometimes the practice to literally circulate the products of combustion over the open crucible or vessel containing the charge. With such designs, in addition to contamination problems, there may be a significant loss of volatile elements from the charge. Such losses are not only objectionable because of the obvious loss of material but also because in the case of alloys, the proportions of the alloy constituents are changed. Finally, the entrainment of vaporized elements from the charge in the exhaust gases of the furnace contributes significantly to air pollution.
There are other problems associated with the operation of conventional crucible furnaces, such as high noise level, health hazards to operating personnel, and the need of cooling towers and special ventilating systems in the structures in which the furnaces are mounted.